1. Field
The present disclosure relates to optical communication equipment and, more specifically but not exclusively, to an optical receiver for quadrature-phase-shift-keying (QPSK) and quadrature-duobinary (QDB) signals.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Polarization-division-multiplexed (PDM) QPSK modulation with digital coherent detection is one of the leading technologies for use in 100-Gb/s optical transport systems. Recently, PDM-QDB modulation has attracted attention, as an alternative to PDM-QPSK modulation, due to its nearly doubled spectral efficiency and better tolerance to channel crosstalk, narrow optical filtering, and chromatic dispersion. However, currently available PDM-QDB receivers are not interchangeable with PDM-QPSK receivers and generally require more complicated digital signal processing.